I wonder if Hawking said that to kinda be taken humourously.
Hawking writes:
I think it will be much more exciting if we don't find the Higgs. That will show something is wrong, and we need to think again. I have a bet of 100 dollars that we won't find the Higgs...
Sounds like something someone would say with a big smile on their face. Sort of like he's "hedging his bets". Finding the Higgs Boson... everyone wins. Not finding it... he says is 'more exciting'. Not 'more likely', just that it would be 'more exciting'.
That's why I think he's only betting $100. I don't think it's meant to be taken as a serious bet of his reputation. More of a joking, bet-hedging hope.
But who knows... it's not like I know the guy